Prefilled syringes are classified into a type in which a plunger is not mounted in advance on a gasket and then mounted on the gasket when the prefilled syringe is used, and a type in which the plunger is mounted on the gasket in advance.
The prefilled syringe in which the plunger is mounted on the gasket in advance can be assembled as follows: after the gasket is inserted into the outer cylinder by using a method called “vacuum capping” in which the gasket is disposed at the opening of the outer cylinder under a pressure-decreased atmosphere (under a vacuum atmosphere) in the state in which a medical agent is filled inside the outer cylinder whose opening disposed at its distal end is sealed, and the plunger is mounted on the gasket at a normal pressure. In a state in which the plunger has been mounted on the gasket, it is relatively difficult to dispose the gasket at the opening of the outer cylinder. Further, it is necessary to additionally take the space in which the pressure is decreased in correspondence to the size of the plunger. Thus, a vacuum capping of a prefilled syringe is performed without mounting the plunger on the gasket. Therefore the prefilled syringe of this type necessitates a plunger-mounting work to be performed subsequently.
In the prefilled syringe of the type in which the plunger is not mounted on the gasket, a user performs an operation of mounting the plunger on the gasket when the user uses the prefilled syringe.
When the plunger is mounted on the gasket by press fit, there is a case in which a pressure generated by the press fit causes the medicinal solution to leak from the gasket or a nozzle of the outer cylinder. Therefore a prefilled syringe in which the gasket and the plunger are coupled to each other by screwing between a female screw formed on the gasket and a male screw formed on the plunger can be used.
There are many cases in which the prefilled syringe is used by mounting it on a syringe pump. The prefilled syringe is set on the syringe pump by mounting a flange disposed at the proximal end portion of the outer cylinder on a holder of the syringe pump and mounting a disk part disposed at the proximal end of the plunger on a fixing groove of a slider of the syringe pump. Some types of syringe pumps have a longitudinal slit for engaging a longitudinal rib with the slider. In such a type of the syringe pump, to fit the rib of the plunger in the longitudinal slit of the slider, it is necessary to make a fine adjustment by rotating the plunger to fit a rib of the plunger in the longitudinal slit of the slider. In the above-disclosed type in which the plunger is mounted on the gasket by using screws, there is a case in which the engagement between the plunger and the gasket is loosened by the plunger-rotating operation.
The prefilled syringe disclosed in European Application Publication No. 1 849 490, International Application Publication WO 2006/087762, has a gasket which slidably obstructs the inside of the barrel where the lure taper part is formed and has the hollow part at the inner circumferential side thereof and the plunger rod. The plunger rod is coupled to the gasket through the anchor part. The anchor part projects from the pedestal part of the tapered surface, which is inclined at the angle of 5 to 45 degrees with respect to the surface of the plunger rod orthogonal to the axial direction thereof and has the distal end contact part, which contacts the back side of the distal end of the gasket and the contact member which is freely fitted on the outer circumferential of the gasket and contacts the inner circumferential wall thereof. The pedestal part has the concave curved surface between the distal-end contact part and the tapered surface. The contact member has the convex curved surface at the portion opposed to the concave curved surface. The barrel has the locking cylinder having the spiral line formed on the inner surface thereof.
The prefilled syringe disclosed in Japanese Patent Application Laid-Open No. 2008-307237 is filled with a medicinal solution and the gasket is inserted into the outer cylinder by the capping work. The prefilled syringe includes the coupler which screws on the proximal end of the gasket, the bottom rod coupled to the coupler at its proximal end, the stopper formed on the coupler, and the engaging part, formed on the bottom rod, which engages the stopper owing to the rotation of the bottom rod in the screwing direction. When the stopper contacts the engaging part in the direction opposite to the screwing direction, the stopper elastically deforms and does not engage the engaging part.
As disclosed in Japanese Patent Application Laid-Open No. 2009-142508, the syringe has the gasket, the outer cylinder, and the plunger. The plunger has the spiral rib formed on the outer surface of the head part. The gasket has the spiral screwing part which screws on the spiral rib, the annular rib, to help prevent the separation of the plunger from the gasket, which is located at a position in the vicinity of the spiral screwing part and distal therefrom, and the accommodation part for accommodating the portion where the spiral rib of the head part of the plunger is formed. The annular rib has the rib-absent portion for guiding the spiral rib which has reached the annular rib owing to the progress of the screwing between the spiral rib of the plunger and the spiral screwing part of the gasket to the accommodation part.
In the prefilled syringes disclosed in Japanese Patent Application Laid-Open No. 2008-307237 and Japanese Patent Application Laid-Open No. 2009-142508, it is necessary to perform a work of rotating the plunger to mount the plunger on the gasket. In the prefilled syringe disclosed in Japanese Patent Application Laid-Open No. 2008-307237, it is not necessary to rotate the plunger to mount the plunger on the gasket, nor to mount the plunger on the gasket by pressing the distal end portion of the plunger into the gasket. But during the work of mounting the plunger on the gasket, there is a relatively high possibility that the distal end portion of the plunger deforms the gasket, thus causing a medicinal solution to leak. In addition, there is a possibility that after the plunger is mounted on the gasket, the distal end portion of the plunger deforms the gasket when the plunger is pressed, thus causing the medicinal solution to leak.